This invention relates generally to the dispensing of fluid materials onto substrates. More particularly, the invention relates to the detection and/or monitoring of a bead of material which has been deposited onto a substrate. Specifically, this invention is applicable to the detection of the presence of discontinuities associated with a deposited bead of material, such as, for example, a bead of an adhesive, sealant, or caulk, as well as determining other qualities of the deposited bead, such as its height, cross-section, or the amount of material that has been dispensed. This invention is especially useful in the monitoring of a bead of material dispensed onto the periphery of window glass, such as a windshield in preparation for adhesively bonding the glass to the body flange of a vehicle.
The presence of an air bubble passing through a nozzle of a dispensing system or a reduction in the material supply pressure may cause a disruption in the flow rate of material being dispensed so as to produce a discontinuity or deformation in the bead deposited upon the substrate. If the air bubble or the reduction in the material supply pressure or flow rate is small, the effect on the resulting bead may be minimal. However, if the air bubble is large or the material supply pressure is insufficient, the effect may produce a significant discontinuity in the bead, or a bead having an insufficient height or cross-section. In some applications, discontinuities in the bead may not be critical, however, in others they may be. For example, discontinuities in a bead of the adhesive/sealant applied to a windshield may not only affect its ability to act as a moisture barrier, but it also may affect the strength of the bond of the windshield in the vehicle.
Attempts have been made to detect gaps in dispensed beads automatically as opposed to an operator's visual inspection. This has included monitoring pressure fluctuation within the system as set forth in U.S. Pat. Nos. 4,662,540 and 5,182,938, as well as monitoring the vibration of the dispenser, such as set forth in U.S. Pat. No. 5,086,640. These patents attempt to detect a discontinuity in the bead before the bead is actually deposited onto the substrate. They only infer that a discontinuity has occurred, as opposed to verifying that a discontinuity has actually occurred in the deposited bead.
Although not in the assembly of automobile glass, sensors have been used to monitor energy radiating from the deposited bead by utilizing an infrared sensor, such as shown in U.S. Pat. No. 5,026,989. However, this device must be used with a heated adhesive, such as a hot melt adhesive. It therefore would not be useful with room temperature adhesives commonly used in the automotive industry.
German Utility Patent G 91 10 924.8 and U.S. Pat. No. 4,376,244 generally teach directing a beam of light onto a substrate before the adhesive is applied and directing the beam of light onto the substrate after the drop of adhesive has been applied. This device monitors only the presence or absence of adhesive on the substrate and does not provide a determination if sufficient material, such as evident by its height and/or width, has been deposited. Furthermore, this device requires a reflective substrate, such as metal or veneer, and may not be suitable for all substrates, such as glass.
Beads that are continuous, but not of a sufficient height or width, may also be undesirable because the ability of the bead to act as a moisture barrier and/or the strength of the bond of the window glass to the vehicle may be affected. In like manner, beads exceeding a certain height or width may also be undesirable. Therefore, it is desirable to be able to determine not only discontinuities in the bead, but also to detect the quality, such as the height, width, etc. of the deposited bead.